Sadly, some downloads cannot be resumed. This is not a limitation in Firefox, but rather imposed by the company offering the download, as they usually don't want you to download a file more than once. The only thing you can do in that case is go back to the page where you got the download from and restart it from there.

There is something you can try when this happens..

Go to your downloads folder location. If the download has failed, Firefox may have created a .part file. If your file is largefile.exe, look out for largefile.exe.part.

Now basically all you have to do is go to the downloads page and start downloading your file again. This time pause the download, go to your downloads folder.

Rename "largefile.exe" to "oldlargefile.exe". Rename "largefile.exe.part" to "largefile.exe" obviously replacing the name with your own file.

Now resume your download. It should continue from where it left off.

what are the options when no .part file created???

mine is crashing at 32mb ... guessing as the internet went slow (3.2kb) as somehow I used 20gb in 3 days... that is what the provider is saying... (who knows how... I only downloaded 1gb))

I am wanting to resume download and I cannot work out how two files one is 50mb, and other is 800mb any ideas?

side note: and I am new to firefox - be great if firefox browser identify my usage so I could have a conversation with my provider

Sorry, I can't help you with an interrupted or incomplete download.

This is the only "net usage" addon for Firefox that I have ever heard of.
http://netusage.iau5.com/